Difference between revisions of "R/C2/Plotting-Bar-Charts-and-Scatter-Plot/English"

Opening slide

Learning Objectives

• Plot bar charts
• Plot scatter plot
• Find the correlation coefficient between two objects

Pre-requisites

https://spoken-tutorial.org

• Data frames in R
• Basics of Statistics

If not, please locate the relevant tutorials R on this website.

System Specifications

• R version 3.4.4
• RStudio version 1.1.463

Install R version 3.2.0 or higher.

Download Files

• A data frame moviesData.csv
• A script file barPlots.R.

Please download these files from the Code files link of this tutorial.

Highlight moviesData.csv and barPlots.R in the folder Plots

This folder is located in myProject folder on my Desktop.

I have also set Plots folder as my Working Directory.

Bar Chart

• A bar chart represents data in rectangular bars with length of the bar proportional to the value of the variable.
• R uses the function barplot to create bar charts.

[Rstudio]

moviesSub <- movies[1:20,]

Save the script and run the current line by pressing Ctrl + Enter keys simultaneously.

Now, we draw a bar chart of imdb_rating for these movies.

barplot(moviesSub$imdb_rating,

ylab="IMDB Rating",

xlab = "Movies",

col="blue",

ylim=c(0,10),

main="Movies' IMDB Rating")

• moviesSub dollar sign imdb underscore rating is the data for plotting
• ylab and xlab for adding labels to the respective axes
• col to set the color of bins
• ylim to set the range of values on Y-axis
• main for adding a title to the bar chart

However, we do not know the name of the movies.

barplot(moviesSub$imdb_rating,

ylab="IMDB Rating",

col="blue",

ylim=c(0,10),

main="Movies' IMDB Rating",

names.arg=moviesSub$title)

Remember, title column in moviesSub contains the names of movies.

But not for all movies.

This is due to the point that the names are too long to be accommodated.

That’s why, we will make these names perpendicular to X-axis.

barplot(moviesSub$imdb_rating,

ylab="IMDB Rating",

col="blue",

ylim=c(0,10),

main="Movies' IMDB Rating",

names.arg=moviesSub$title,

las = 2)

Highlight las in the Source window

las equal to 2 produces labels which are at right angles to the axis.

For example, Filly Brown has an IMDB rating of approximately 6.

We can add more arguments to barplot function for adjusting labels.

For more information, please refer to the Additional Material section on this website.

For this, we will draw a scatter plot with these two objects by using plot function.

Remember, we have already learnt how to plot a single object.

Scatter Plot

• The pattern of the resulting points reveals the correlation.

plot(x = movies$imdb_rating,

y = movies$audience_score,

main = "IMDB Rating vs Audience Score",

xlab = "IMDB Rating",

ylab = "Audience Score",

xlim = c(0,10),

ylim = c(0,100),

col = "blue")

For this, we use cor function.

cor(movies$imdb_rating, movies$audience_score)

A positive value indicates that the variables are positively related.

Summary

• Plot bar charts
• Plot scatter plot
• Find the correlation coefficient between two objects

Assignment

• Read the file moviesData.csv. Create a bar chart of critics underscore score for the first 10 movies.
• Create a scatter plot of imdb underscore rating and imdb underscore num underscore votes to see their relation.
• Save both the plots.

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Acknowledgment

Thank You

This is Sudhakar Kumar from IIT Bombay signing off. Thanks for watching.